<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .circle {
      position: relative;
      width: 200px;
      height: 200px;
    }

    .circle:before {
      content: "";
      position: absolute;
      top: 50%;
      left: 50%;
      transform: translate(-50%, -50%);
      width: 20px;
      height: 20px;
      background-color: #f00;
      border: 10px solid yellow;
      outline: 10px solid green;
      /* 是不是没用*/
      /* box-shadow: 0 0 0 20px #000, 0 0 0 4px #0b8e60, 0 0 0 30px yellowgreen; */
      /* box-shadow: 0 0 0 20px #000, 0 0 0 30px yellowgreen; */
      box-shadow: 0 0 0 20px #000, 0 0 0 30px yellowgreen, 0 0 0 40px rgb(212, 7, 28), 0 0 0 50px rgb(50, 5, 230);
      border-radius: 50%;
    }

    /* .element:before {
      content: '';
      position: absolute;
      top: 50%;
      left: 50%;
      width: 100px;
    height: 100px;
    border-radius: 50%;
    background: radial-gradient(circle at center, red 0, red 20px, orange 40px, yellow 60px, green 80px, blue 100px);
    transform: translate(-50%, -50%);
    }
    */

    /* .element:before {
      content: '';
      position: absolute;
      top: 50%;
      left: 50%;
      width: 50px;
      height: 50px;
      border-radius: 50%;
      box-shadow: 0 0 0 10px red, 0 0 0 20px orange, 0 0 0 30px yellow, 0 0 0 40px green, 0 0 0 50px blue;
      transform: translate(-50%, -50%);
    } */

    .element {
      position: relative;
      width: 200px;
      height: 200px;
    }

    .element::before {
      content: '';
      display: block;
      position: absolute;
      left: 50%;
      top: 50%;
      transform: translate(-50%, -50%);
      width: 20px;
      height: 20px;
      border-radius: 50%;
      background: red;
      box-shadow:
        0 0 0 5px orange,
        0 0 0 10px yellow,
        0 0 0 15px green,
        0 0 0 20px blue;
      box-shadow:
        0 0 0 10px orange,
        0 0 0 20px yellow,
        0 0 0 30px green,
        0 0 0 40px blue;
    }
  </style>
</head>

<body>
  <div class="circle " style="margin-top: 50px; margin-left: 50px;"></div>
  <div class=" element" style="margin-top: 50px; margin-left: 50px;"></div>

</body>

</html>